1. Field of the Invention
The present invention relates to a method of the forming a conformal oxide film, more specifically, to a method of forming a conformal silicon oxide film through repetitious deposition-oxidation processes. The method can be applied to form phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG) as well by doping phosphorus (P) or boron (B) into the polysilicon layer prior to the oxidation process.
2. Description of the Prior Art
Silicon oxide, having a proper dielectric constant and excellent cohesion to silicon surfaces, is commonly used for gate oxide, local oxidation of silicon (LOCOS), field oxide, interlayer dielectric, pad oxide, etc. As the integration density of the electrical devices fabricated on the wafer increases, the standard for the quality and the step coverage ability of the silicon oxide becomes more rigid.
There are three commonly adopted methods for forming a silicon oxide film on the surface of a semiconductor wafer: (1) chemical vapor deposition (CVD), (2) thermal oxidation, and (3) spin-on glass (SOG). The CVD processes include silane low-pressure chemical vapor deposition (SiH4-LPCVD), tetra-ethyl-ortho-silicate low-pressure chemical vapor deposition (TEOS-LPCVD), plasma-enhanced chemical vapor deposition (PECVD), etc. Generally a silicon oxide film formed by the CVD process has better step coverage ability and a film formed by thermal oxidation has better etch resistance. However, with the improvement of semiconductor processes, semiconductor device volumes are decreasing, so that the step coverage ability of silicon oxide formed by the CVD process needs to be improved significantly.
Please refer to FIG. 1. FIG. 1 is an enlarged cross-sectional view of a tiny structure 10 on the surface of a semiconductor wafer. For simplicity of description, other devices on the semiconductor wafer are omitted in FIG. 1. As shown in FIG. 1, the tiny structure 10, having a silicon oxide thin film 14 deposited by a TEOS-CVD process on the surface, is a protrudent structure with two approximately vertical walls 12. Though having excellent step coverage ability, the silicon oxide thin film 14 formed by the TEOS-CVD method is not deposited via a surface-reaction mechanism, so that portions of the silicon oxide thin film 14 in the corner area 16 can not be conformal, as is needed in many product applications.
It is therefore a primary objective of the present invention to provide a method of forming a conformal oxide film on a semiconductor wafer.
It is another objective of the present invention to provide a method of forming a conformal silicon oxide thin film with excellent step coverage ability and etch resistance.
It is another objective of the present invention to provide a method of forming a conformal silicon oxide thin film on uneven surfaces of tiny structures of the semiconductor through repetitious deposition-oxidation processes.
It is another objective of the present invention to provide a method of forming a conformal thin film, composed of phosphosilicate glass (PSG) or borophosphosilicate glass (BPSG), as well as to provide combinations of complex films composed of various silicate glasses.
It is another objective of the present invention to provide a method of forming an oxide film on an oxide-nitride-oxide (ONO) dielectric layer.
According to the claimed invention, a substrate of a semiconductor has at least one tridimensionally tiny structure. At the beginning of the method, a conformal first silicon film is deposited on the tridimensionally tiny structure. The first silicon film is then completely oxidized to form a conformal first oxide film on the tridimensionally tiny structure. By performing a deposition process, a conformal second silicon film is formed on the first oxide film. Finally, the second silicon film completely oxidized to form a conformal second oxide film on the tridimensionally tiny structure at the end of the claimed invention.
It is an advantage of the present invention that the present invention provides a method of forming a conformal silicon oxide film, with excellent step coverage ability, on uneven surfaces of tiny structures of the semiconductor through repetitious deposition-oxidation processes. Additionally, the present invention provides a method of forming a conformal thin film, composed of PSG or BPSG, or combinations of complex films composed of various silicate glasses.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the multiple figures and drawings.